Research is being conducted in an attempt to realistically model smoke and/or obscurant clouds for use in simulations of real and artificial scenes. For the simulation of real clouds in two dimensions, it is desirable to know the two-dimensional field of view of the observer, the two-dimensional distribution of aerosol concentration in the cloud to be simulated, the aerosol radiance of the cloud to be simulated, and the path radiance of the cloud to be simulated due to scattered radiation. These parameters, except for path radiance due to scattering, can be obtained using the Atmospheric Transmission Large-Area Analysis System (ATLAS).
ATLAS is disclosed in an article entitled "Analysis and Assessment of the Atmospheric Transmittance Large Area System (ATLAS)," by Haar Vonder, T. G. Stephens, A. Jones, C. F. Shih, and J. Davis, of Metsat Inc., Fort Collins, Colo., in 1990, and in another article entitled "A Comparison of the MPTR and ATLAS Transmissometers," by M. P. Bleiweiss, R. Howerton, R. Valdez, K. Payne, T. King, and K. Hutchison, in 1991, in the Proceedings of the Smoke/Obscurants Symposium XV, U.S. Chemical Research Development and Engineering Center, Aberdeen Proving Ground, Md. 21010. ATLAS allows real smoke clouds to be extracted from a scene and saved for later insertion into real or artificial scenes.
ATLAS uses a simplified form of an equation of radiative transfer applied to infrared imagery to produce a two-dimensional transmittance map of a cloud and the cloud radiance in a plane perpendicular to the line of sight of an observer. The present invention operates on any scenes, using the derived radiance and transmittance of the cloud to arrive at a new scene with the cloud affects present in a physically correct manner.
An equation for radiative transfer to infrared imagery is as follows: EQU LR(i,j)=LO(i,j)T(i,j)+LC[1-T(i,j)]+LS(i,j),
where LO(i,j) is the radiance from scene element (i,j) in clear air, T(i,j) is the transmittance of the smoke cloud for the (i,j) scene element, LC is the radiance of the smoke cloud due to the thermal emission of the aerosol that makes up the cloud, and LS(i,j) is the path radiance due to scattering. ATLAS simplifies this equation by ignoring the path radiance due to scattering. This does not mean that path radiance due to scattering is not important. Path radiance is ignored because it is difficult to account for and is many times a small affect. The simplified equation can be rearranged to yield the following expression for transmittance: EQU T=(LR-LC)/(LO-LC).
Whereas the present invention deals with adding real clouds to simulated or real two-dimensional scenes, the following four articles deal with creating artificial clouds in simulated two-dimensional scenes: "Visualization of Battlefield Obscurants," by G. Y. Gardner and G. M. Hardaway, 1992, in Proceeding of the 1991 Battlefield Atmospheric Conference; "Theoretical and Measured Fractal Dimensions for Battlefield Aerosol Cloud Visualization and Transmission," by D. W. Hoock, 1992, in Proceedings of the 1991 Battlefield Atmospheric Conference; "Modeling Time-Dependent Obscuration for Simulated Imaging of Dust and Smoke Clouds," by D. W. Hoock, 1991, in SPIE Vol. 1486 Characterization, Propagation, and Simulation of Sources and Backgrounds, pp. 164-175; and "Improved COMBIC and Fractal Smoke Models for Use in the TACOM Thermal Image Model (TTIM)," by F. G. Smith, C. S. Hall, T. J. Rogne, and J. L. Manning, 1990, in Proceedings of the Tenth Annual EOSAEL/TWI Conference.
U.S. Pat. No. 4,493,647, entitled WEATHER RADAR SIMULATOR, discloses a device for simulating a weather radar in an aircraft simulator. The device of U.S. Pat. No. 4,493,647 generates a radar signal for different cloud formations that are stored in a memory device. U.S. Pat. No. 4,493,647 does not add real clouds to a simulated two-dimensional scene as the present invention does.
U.S. Pat. No. 5,192,208, entitled RADAR SIMULATION FOR USE WITH A VISUAL SIMULATOR, discloses a device for and method of producing visual images of terrain along with a radar image of the same terrain. U.S. Pat. No. 5,192,208 does not add real clouds to a simulated two-dimensional scene, have the ability to change the composition of the clouds, or have the ability to move the clouds with respect to meteorological conditions or topography as the present invention does.
U.S. Pat. No. 5,135,397, entitled 3-D WEATHER FOR DIGITAL RADAR LANDMASS SIMULATION, discloses a device for and method of compressing/decompressing weather-pattern data for use in a digital radar landmass simulator. U.S. Pat. No. 5,135,397 does not add clouds to a simulated two-dimensional scene as the present invention does.